Seventh Circle Audio

I have heard a lot of good things about the preamps on this website.
I was just ready to order a pair of J99s plus powersupply when a technician-friend created a doubt about assembling my first own high end preamp.
He said that the tolerance of the transistors , resistors etc would be the main problem in getting a preamp that is truly top notch. A high end preamp should have handselected/ tested parts. Otherwise the desired quality would not be achieved.
That person said also that it easily happens to somebody who is not an expert in soldiering to spoil the transistors , etc ( by exposing them to too much heat?) which can leed to malfunctions or spoiled parts .
Of course, the right answer would be that all this is nonsense and I dont have to worry about it.
But please give me some evidence about your opinion.
Veet

I wouldn't worry about your friend's warnings too much...I don't think anyone has ever ended up with a non working SCA pre yet.

As far as the transistors...Use the recommended soldering equipment and eutectic solder and you'll be fine. Transistors can handle quite a bit of heat without a problem.

Shane

Say i build two identical preamps. I deliver them to studios, one in Brooklyn and the other in San Francisco (just for arguements sake). One studio may be operating at 123VAC, the other at 112VAC, different ambient temperatures, humidities, they all have different microphone cables and microphones which all have different specs. So whats the point of having the identical pre amps when everything around them is different?

With amplifier design the tolerances of the components are known before the design begins. The design is "built" around these tolerances. There are tolerances with everything, building materials, cement, semiconductors, everything... good design makes it work regardless.

Don't forget that most transistors are binned according to output, and as long as you buy the same spec you are likely lose enough for most circumstances (except maybe matched input pair situations like op amps, etc.).

Tim knows what he is doing. The preamps will sound the same and gain should be within a fraction of a dB too.

Shane

Thanks for answering so far.
I feel like going for it. There is not really that much to loose.
I ll start with one or two amps with the option put more channells into the box. :

read up on how to solder. your kit will benefit from that. practice before you start on the real deal.

bb

He said that the tolerance of the transistors , resistors etc would be the main problem in getting a preamp that is truly top notch. A high end preamp should have handselected/ tested parts. Otherwise the desired quality would not be achieved.

It's hard to know where to start with a comment like this, since it leads straight to audiophile ridiculousness. The questions you might want to think about instead are: What is the definition of a "truly top notch" preamp? What is the type and degree of "desired quality" that may or may not be achieved? What methods of evaluation will be applied to determine the degree of achievement? And what does component tolerance have to do with any of it?

From a rational engineering perspective, the measure of success is meeting a set of specifications, no more, no less. If the only way to meet the specification is to use tight tolerance parts or hand match components, then that's what you do. Whenever possible, circuits are designed to meet specifications with the most common parts and simplest assembly methods.

That person said also that it easily happens to somebody who is not an expert in soldiering to spoil the transistors , etc ( by exposing them to too much heat?) which can leed to malfunctions or spoiled parts .
Of course, the right answer would be that all this is nonsense and I dont have to worry about it.
But please give me some evidence about your opinion.

This is worth worrying about, though only a few kitbuilders have actually damaged components during assembly. As mentioned above, if you have doubts about your soldering skill, practice on some surplus parts or an inexpensive kit before attempting one of ours.